This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Blood coagulation is ensured through equilibrium between pro- and anti-coagulant coagulation factors that interact with each other and cells. Factor VIII (FVIII) is a large multidomain protein (~280kDa), which in its active form, Factor VIIIa (FVIIIa) acts as a co-factor to the serine protease Factor IXa (FIXa) within the membrane-bound Tenase complex. Binding of FVIIIa to FIXa onto the platelet surface increases Factor Xa (FXa) and Thrombin generation more than 10^6 times. Mutations in FVIII result in mild to severe Haemophilia type A, a life-threatening blood condition affecting one in 5000 of the male population (Wacey et al., 1996). The sole cure for this condition is intravenous administration of FVIII, whose membrane-bound structure has been studied by Stoilova-McPhie using cryoEM. Our goal is to define the active conformation (structure) of the membrane-bound complex(es) of blood coagulation factors essential for the aniticoagulant pathways of blood hemostasis. Our approach is to organize them helically (onto) a lipid nanotube and define (their) membrane-bound structure (combining) Cryo-EM and image reconstruction.